Removing the Tone Control from a TS type circuit ...

[Melanhead]

I was playing around with a bare bones tubescreamer ( similar to Jack's Son Of A Screamer ) and it dawned on me that when I set the tone on this thing I try to match the same treble response of the amp. I know the boss OD-1 didn't have a tone control and I rather like it.

Is it as easy as removing both .22 caps, the pot and the 220 omh resistor or am I missing something ?

[vanessa]

I'm with you on this one. I would like to know as well.

I don't like how the stock tone control E.Q.'s the effect and would like to do without. I know the Boss OD-1 did this, would I just sub those values in for a Tube Screamer build (minis the tone control)?

[cd]

Replace the tone pot with two 10k resistors, simulating the tone pot in the exact "middle" position (no cut, no boost).  That's what the 2nd opamp stage in an OD-1 does.

[johngreene]

Looks like the OD-1 was an inverting circuit according to this schematic:


But to emulate that with a TS808 type circuit would minimally involve removing the leads to the tone control and lifting the .22uF connected to the non-inverting input.

--john

[cd]

But to emulate that with a TS808 type circuit would minimally involve removing the leads to the tone control and lifting the .22uF connected to the non-inverting input.

But then you get lots of screechy highs.  That .22u kills the highs above 723Hz, just like the combination of R10 and C6 in the OD-1 schem posted above (slight different turnover frequency of 884Hz but same thing accomplished - cut harsh harmonics).

[vanhansen]

Melan, funny you mention this.  I'd rather use the amp's tone stack too.  If it has a tone control, fine, it's not an end all but I would cry if it didn't either.  This is exactly why I left a tone control of my Sixteen Overdrive and Slapshot Booster/Overdrive (cheap plug, I know..lol).  I just sat there and tweaked until it sounded right to me.  The Slapshot is very much TS based.

[Mark Hammer]

It never dawned on me before, but the .22uf cap and 220R resistor connected to the wiper of the tone control provide a common path to ground for two points of the circuit.  One of them is the ground leg of the gain-setting resistance in the tone stage.  The other is the lowpass filter formed by the 1k/.22uf combo after the clipping stage.

If you rotate the tone control all the way to one end, then the .22uf cap and 220R resistor are placed in parallel with the .22uf cap to ground after the clipping stage.  You have essentially doubled the capacitance in that simle lowpass filter, albeit with the complications of a series resistor but we'll ignore that for the moment.

At the same time, the full resistance of the tonepot is added to the ground leg of the non-inverting stage fomed by the second op-amp.  That op-amp has a 1k feedback resistor, and 20k+220R going to ground.  Not much gain there (just a shade over x1), but the low-end rolloff is around 36hz.

Rotate the tone pot the other way completely, and that ground leg is now the .22uf cap and 220R resistor alone.  Calculating the gain and rolloff for the tone stage, we see that gain is now about x5.5 and the low-end rolloff is around 3.3khz.  Meanwhile, the lowpass filter formed by the 1k/.22uf combo is paralleled with a 20k resistance going to the .22uf/220R path to ground, so not much treble-cut help there.  Although there is a gain changeas the tone control is rotated, the loss of overall amplitude by cutting the low end makes it feel like the volume has remained relatively constant.

So, what can you do to exploit this?

1) Cut the connection between the 1k/.22 combo and the tone control.
2) Replace the .22 cap with a 1uf cap.
3) Swap the 1k feedback resistor for 2.2k.

What do you have now?

You have a clipping stage with a simple lowpass filter (1k/.22uf) after it, followed by a non-inverting gain stage that can increase the overall output by x11.  This added stage provides no treble boost.  When the tone pot is set to max resistance, it adds little gain and negligible bass rolloff.  As that resistance is decreased and gain increased, the low end is gradually shaved until at max gain, there is a low-end rolloff around 720hz, which is more or less compatible with the "nature" of the TS-9, though a tad thin for some folks.  You may want to consider sticking in a 2.2uf cap instead if girth is your game.  If the fizz still bugs you, put a .01uf cap in parallel with the 2k2 you've installed.

You now have a TS with substantially more output than a stock one, and a gain control that behaves somewhat like that of a Dist+/DOD250 where the low-end depends on the gain. Fortunately, you can crank this second gain to shave the bass, and tame the level with the standard volume control.  So, two gain controls and a master output level.

Thanks.  That was a productive question for me.

[Elektrojänis]

How about ditching the whole tone control stage like the Tube Reamer. Tweak the 0,033µF capacitor (0,22µF in the TS) for different treble response.

If you don't like the way the gain control is arranged  (cut's more bass when the gain is higher) you can change it to stock TS-style.

Actually in stock TS the treble responce is somewhat flat (at least above 3.2kHz anyway) when the tone control is at maximum treble because it will boost the response where the 1kohm/0.22µF cuts). Check out GEO Technology of the tube screamer (the part "Tone and volume control stages") if you didn't allready.

[Mark Hammer]

You could, but if you have one already built, it's easier to just swap a couple of parts and cut a connection than to start doing more major changes.  Besides, isn't one of the common complaints about the TS that it doesn't have enough output level?

[vanessa]

I wanted to build a new one from scratch without the tone control, but have it sound normal not muffled. I would enjoy a little more output out of it too!

[Melanhead]

Gee! ... thanks for all the input guys, and Mark, wow! ... I was sorta thinking along the lines of using that 2nd stage for more gain so you've sorta answered that question too ... no sense in wasting half an op-amp

The whole thing for the idea was basically to build an overdive with minimal parts that sounded good and was fairly transparent. ( I know, there's that word again, but a friend used it to describe what he wants me to build for him ... basically his tone with distortion added, no coloration. )

I was thinking that I'd probably have to keep the low-pass in there even if I did remove the tone control ...

Oh well, I guess I'll have to do some experimenting over the holidays!

thanks again ...

EDIT: Okay know I've taken a peak at the schematic, and although I was originally gonna use the second part of the op-amp as a fixed gain stage I now see exactly what you're talking about Mark ... I've often thought it would be a cool idea to do the same type thing in the first stage ( remove the 4.7K res in the clipping stage and add a 10k pot in series with a 1k res ) just to see what kind crazy gain I'd get. The frequency response would change with the changing resistance and fixed cap  ( .047 )  but it would be a cool experiment

[Melanhead]

You could, but if you have one already built, it's easier to just swap a couple of parts and cut a connection than to start doing more major changes.  Besides, isn't one of the common complaints about the TS that it doesn't have enough output level?

Exactly we're I was going ...

[Melanhead]

Melan, funny you mention this.  I'd rather use the amp's tone stack too.  If it has a tone control, fine, it's not an end all but I would cry if it didn't either.  This is exactly why I left a tone control of my Sixteen Overdrive and Slapshot Booster/Overdrive (cheap plug, I know..lol).  I just sat there and tweaked until it sounded right to me.  The Slapshot is very much TS based.

I guess this mostly comes from the mentality "the less junk in the signal path, the better! " ... or at least with me it does, Plus it saves a pot on every build and some parts too

[MartyMart]

I guess this mostly comes from the mentality "the less junk in the signal path, the better! " ... or at least with me it does, Plus it saves a pot on every build and some parts too

http://aronnelson.com/gallery/Martys-layouts-and-photos/MrDrive?full=1

Shameless plug !!
This is more "Dist +" - like,  but will get you to "clean" through "TS" to "Distortion"
without much colouration.
It's a fine sounding " two knob" circuit ...

MM.

[vanessa]

I guess this mostly comes from the mentality "the less junk in the signal path, the better! " ... or at least with me it does, Plus it saves a pot on every build and some parts too

http://aronnelson.com/gallery/Martys-layouts-and-photos/MrDrive?full=1

Shameless plug !!
This is more "Dist +" - like,  but will get you to "clean" through "TS" to "Distortion"
without much colouration.
It's a fine sounding " two knob" circuit ...

MM.

I'm with you both!

Marty, does this circuit have a lot of output?

[MartyMart]

Yes, Mr Drive has plenty ... if you want it a bit "less subtle" and more output, just
use 100k pots for both gain & volume, I think that's what i ended up using. ( both log )
I have three out there, being gigged on a regular basis 
There are sound samples, if you search "Mr Drive"  you'll get to a few.
My best sounding OD's and Fuzz's are indeed "simple"  !!

MM.

[Melanhead]

Thanks Marty! ... that's sorta the idea ... nice and simple so they fit in a "B" size box ... takes up less room on the pedal board, and mine is getting pretty full! 

[Mark Hammer]

Viewers will note that since the Mr. Drive puts gain control into the feedback loop (as the TS and SD-1 do), rather than in the ground leg (as the Dist+ and 250 do), increasing the gain also shaves off more high end, using the formula rolloff = 1/[2*pi*.00012uf*setting-of-pot].  The amount of "treble-shave" is quite limited, however, because the 120pf cap is kinda small (max cut is at a rolloff of 26khz).  The Dist+ and 250 both include caps in parallel with the clipping diodes; something which Marty has omitted here (I assume this fits his tastes).  Melanhead and Vanessa might want to consider increasing that 120pf cap to 1000pf, such that when gain is maxed (x107), more treble is shaved before hitting the diodes.  The effect is not exactly the same as use of a cap in parallel with the diodes, but shoul get more of the smoothness that people normally want a TS for.

[Melanhead]

So is this what you meant Mark ?:




I also came up with this although I'm not sure if I'm thinking right



Anyways, ain't this fun!

[Mark Hammer]

So is this what you meant Mark ?:

Yes, although don't forget the 10k biasing resistor to the noninverting input that is normally there.  I doubt whether the second circuit with the additional gain control  is really necessary.  The tenfold increase in level from the first circuit is more than sufficient.  Remember, you've already boosted the signal up enough so that the diodes clip in that first stage.  Even a small amount of gain in the second stage will be easily noticed/felt.

If you feel like doing a re-clip thing, I'd suggest softening it by, say, sticking a resistance in series with the 2nd diode pair (try 1k).  I *am* a big fan of double-clipping, but in this case you end up going in a very different direction than the TS is intended for if you just crank the gain of the second stage and stick more diodes in there exactly like the first stage..